Myotonic dystrophy (MyD) is a multisystemic genetic disease inherited as an autosomal dominant trait and characterized by variable penetrance and pleomorphic expression. This proposal describes experiments attempting to define the biochemical defect(s) in MyD. Experiments are designed to isolate and characterize an erythrocyte membrane glycoprotein shown to be abnormally phosphorylated in MyD. Isolation techniques employ lectin specific affinity chromatography and high pressure liquid chromatography peptide analysis. Identification of a structural abnormality of an intrinsic membrane glycoprotein that may have altered transport functions could lead to delineation of the mechanisms of penetrance and expressivity, and the development of specific preclinical diagnostic methods and preventive treatment.